Analyst Man
ArboristSite Guru
You really have to run this experiment in your mind 'cause you can't cut the same wood twice.
In my thought experiment I cut the same 12" diameter log twice; once with a 16" bar and once with a 20" bar. So the only thing that changed was the length of the bar. Everything else is exactly the same. If you can suspend disbelief a little further you could run the experiment using a chain of zero mass and frictionless contact between the chain and bar. In this scenario there would be absolutely no difference in cutting speed between the long and short bars. This is true because the same volume of wood is removed in each cut. There is no more friction using the long bar than the short bar because there is the same amount of contact between the wood and the chain/bar. Makes sense right?
Now if we take into account the mass of the chain and the friction between the chain and bar, we can agree that the longer bar uses a more massive chain and that there is more more surface area and thus more friction between the chain and bar. Thus greater percentage of the saw's energy is used to simply move the chain around the bar and less of the energy goes into actually cutting wood. So the shorter bar would be the faster.
Real world, the extra mass of the chain and the added friction of the longer chain/bar combo is probably insignificant when compared to the friction between the chain and the wood. I doubt you could even measure the difference even with a stopwatch.
All that other stuff about less bending, fewer cutters to sharpen, less weight, balance between power head and bar, personal comfort, etc. are probably all more important than the difference in the speed of cut.
:agree2:
Bogiemsn, right on, that’s the point I was making in my opening question when I said, “Since the Linear speed of the chain can be no faster than the circular speed of the drive sprocket why do some say that a shorter bar cuts faster?”
So we really don’t gain much cutting speed by using a smaller bar, ok, maybe a little if we consider the additional friction, but not enough to really matter. It sounds like it just boils down to a matter of preference and cutting conditions.